The present invention relates to tubular belt conveyors and, in particular, to a prestressed, self-closing tubular conveyor belt and to the components and to the overall construction of a high speed conveyor system which uses such a tubular belt.
In general, the term tubular belt or tubular conveyor belt refers to a belt which typically has a relatively narrow width compared to its length and which is rolled or formed along its width into a closed tube with overlapping longitudinal edges. Preferably, when used in material transporting systems, such tubular belts are formed as endless conveyors in which pourable material is loaded at one point and dispensed at a second point.
For a number of reasons, conventional tubular conveyor belts have not fulfilled their potential for use in material transport. First, conventional tubular belts require cumbersome external guides, such as radially arranged rollers or funnels or stiff outer tubes, to form and maintain their tubular configuration and to keep the belt edges closed. In addition, these tubular belt conveyors are subject to twisting, despite the use of external shaping devices. If the joint formed by the overlapped belt edges is twisted from the preferred vertical position to a downward-facing position on the lower half of the tube, the belt edges may separate, allowing spillage of the bulk material carried by the conveyor.
Conventional tubular belt conveyor systems use a lumped drive system comprising a cylindrical drive pulley at one end of the conveyor belt, a second cylindrical stretching pulley at the opposite end of the belt, and a set of supporting pulleys or other supports along the lines of the system. This construction has many of the known disadvantages of flat belt conveyor systems. That is, the use of the single, lumped drive to pull the entire conveyor line results in extremely high longitudinal tensions in the belt, especially on ascending slopes. The maximum conveyor length is limited by the tensile strength of the conveyor belt. The high tensile stresses in the belt require heavy reinforcement, and any attempt to lengthen the conveying lines requires even greater, heavier and typically more rigid and expensive reinforcement. In addition, the high torque capacities required of lumped drive systems to pull such heavy and perhaps heavily reinforced conveyor lines usually requires the installation of a speed reduction transmission, which results in additional energy losses.
Furthermore, high speed loading and unloading of a normally closed high speed tubular belt conveyor is difficult. The normally closed belt must be opened and closed for both loading and unloading. In addition, efficiency in the conveying process requires high conveyor belt speeds and requires that the material be loaded through the opening onto the fast moving conveyor belt, transported by the belt, and off-loaded, all without spillage of material.
In short, the construction of conventional tubular belt conveyor systems limits their speed and length, limits the number and degree of turns in such systems, and makes difficult high speed efficient loading of such systems.